Thermal machine

ABSTRACT

Thermal machines are known in prior art. They generally differ considerably from the theoretically most advantageous engine in respect of pressure-volume cycles or have a complicated structure. The object of the present invention is to eliminate these drawbacks and achieve a new type of thermal machine. The advantages of the invention include a nearly ideal phasing of pressure-volume cycles, built-in power regulation and insignificant mechanical losses. This is achieved by using inversely linked connecting rods ( 9 ), four-chamber cylinders and a crankshaft ( 7 ) provided with rolling contact bearings with insertable rolling elements.

The present invention relates to a thermal machine as defined in thepreamble of claim 1.

A thermal machine functioning in accordance with the closed Camot cycleprocess can be used as an engine or as a refrigerating machine dependingon whether the machine is started using thermal energy or mechanicalenergy. The working gas is contained in a closed system in the machine.

To produce useful thermodynamic processes, the gas undergoes in thevarious chambers in the machine the phases of compression, transfer,expansion and restoration to the original state. The efficiency of themachine depends on its phasing precision. To implement the phase shiftbetween the pistons, e.g. a rhombic crank mechanism functioning with twocrankshafts and a lever mechanism has been developed.

Prior art engines have the drawback that, in respect of pressure-volumecycles, they differ considerably from the theoretically mostadvantageous values or that they are complicated. Moreover, in enginesprovided with a complicated rhombic crank mechanism, the cyclic phasingis inaccurate.

The object of the present invention is to achieve a new type of thermalmachine that is free of the drawbacks described above. To implementthis, the thermal machine of the invention is characterised by what ispresented in the characterisation part of claim 1.

The advantages of the invention can be regarded as consisting in thenearly ideal phasing of pressure-volume cycles, small mechanical lossesand relatively simple structure. With the solution of the invention, andaccurate phasing of the cycle process is achieved by using a “stretched”top dead position of the pistons. In addition, the built-in powerregulating circuit of the invention is simple to implement.

In the following, the invention will be described in detail by the aidof an example by referring to the attached drawings, wherein

FIG. 1 is a graph illustrating the operation of the thermal machine ofthe invention,

FIG. 2 presents the structure of the thermal machine of the invention,sectioned along a plane passing through a piston, and

FIG. 3 presents a schematic diagram of the power regulation system usedwith the thermal machine of the invention.

The thermal machine presented in the figures is a five-cylinder(cylinders 21-25 in FIG. 1) Stirling engine.

The cross-section in FIG. 2 shows a cylinder with four chambers: hotchamber 1, compression chamber 3 and pressure equalisation chambers 2and 4, which are interconnected (FIGS. 1 and 3). The compressionchambers 3 are connected to the hot chambers 1 with a 144° delay (FIG.1). The pistons 26, 27 are attached to the same piston rod 6. The pistonrod 6 is provided with a sealing 29 between pressure equalisationchamber 4 and the crankcase 28, and the connecting rod 9 is linked tothe piston rod 6 in an inverted manner, i.e. not in the direction of thepistons, via a fork 6 a and a bracket 8.

The inversely linked short connecting rod 9 enables accurate phasing ofthe cycle process because of the “stretched” top dead centre the volumeof the hot chamber 1 and compression chamber 3 is smallest at the gentlecrest h of the piston motion curves in FIG. 1. When the pistons in thefirst cylinder 21 are in the low position, the pistons in the thirdcylinder 23 are in the top position (FIG. 1). When the crankshaftrotates through 72°, the volume of the compression chamber 3 is doublyreduced whereas the volume of the hot chamber 1 remains the same(isothermal phase, cylinders 22, 24). In the next 72° interval, thecompressed gas is passed from the compression chamber into the hotchamber at the same volume (isochoric phase, cylinders 23, 25). In thenext 72° interval, the gas expands isothermally in the hot chamber; thevolume of the compression chamber does not change (cylinders 24, 21). Inthe last 144° interval, the gas is passed from the hot chamber into thecompression chamber at the same volume (isochoric cooling, cylinders 25,22, 21, 23). The compression ratio in the compression chambers 3 dependson the number of cylinders and relative length of the connecting rods.Instead of a fork 6 a and bracket 8, it is possible to use atwin-crankshaft structure with two connecting rods and a T-joint to thepiston rod.

The schematic diagram (FIG. 3) illustrating the power regulation systemof the Stirling engine shows a power regulation unit 31 used for powerregulation. It interconnects chambers 2 and 4 of each cylinder, and itis also connected to a pressure reservoir 32. In addition, the chambersof the cylinders are connected to each other as shown in FIG. 3.

In the power regulation unit 31, chamber 2 of each cylinder is connectedvia valves 13 to chambers 4 so that the gas will flow through the valvesfrom chamber 4 into chamber 2. Chambers 4 are connected via aspring-loaded regulator valve 11 to the pressure reservoir 32 and viapressure-controlled variable check valves 12 to chambers 2. Valves 13act as pump valves.

The output power is controlled by increasing and decreasing the amountof gas circulating in the engine, as follows:

The total volume of chambers 2, 4, which are interconnected via thepower regulation unit 31, remains practically unchanged. At maximumpower, chambers 2 and 4 as well as the pressure reservoir 32, are atequal pressure. To reduce the power, the spring pressure of the checkvalves 12 is reduced and free flow between chambers 2 is prevented whileat the same time chambers 2 are forced to act as pumps. The working gasis passed from chambers 2 and 4 into the pressure reservoir 32. Thepressure in the compression chambers is equalised with the pressure inchambers 2 and 4 when the pistons are in the low position as chambers 3and 4 are interconnected via channels 5. At the same time, the channels5 eliminate the negative effects of gas leaks.

When the reservoir pressure and the control pressure exceed the springpressure of valve 12, valves 12 are opened and the engine will work atthe selected power level. The power is increased via valve 11. Byreducing the spring pressure of the valve, gas at positive pressure willflow from the reservoir 32 into the engine and be distributed in thesame way as when the power is being reduced. When the spring pressureexceeds the overpressure in the reservoir, valve 11 will be closed.

To reduce mechanical losses and to avoid starting damage, the crankshaft7 is provided with rolling bearings 30 with insertable roller elements.The outer rings of the main bearings as well as the connecting rods areslid onto the crankshaft, whereupon the roller elements are inserted viagrooves 10. The sealing 29 on the piston rod is an accordion-typespiral, one half of which is dextrorse and the other sinistrorse. Thespring-like structure also reduces the static imbalance due to theprojecting piston rod.

What is claimed is:
 1. Thermal machine which operates in accordance witha closed cycle process principle, comprising a cylinder with a hotchamber separated from a first pressure equilisation chamber by a firstpiston, and a compression chamber separated from a second pressureequilisation chamber by a second piston, the first and second pistonsbeing attached to a piston rod, a connecting rod linked between acrankshaft and the piston rod in an inverted manner so that a volume ofthe hot chamber and the compression chamber is smallest at a gentlecrest formed in a motion curve of the pistons.
 2. Thermal machine ofclaim 1, wherein the pressure equilisation chambers below the pistonsare pressurized and have a pressure equal to a pressure in thecompression chamber when the pistons are in a low position.
 3. Thermalmachine of claim 1, wherein the pressure equilisation chambers below thepistons act as a power regulating compressor and as a pressurizingchamber in conjunction with the compression chamber.
 4. Thermal machineof claim 1, wherein the crankshaft is fitted with insertable rollingelements.
 5. Thermal machine of claim 1, wherein there are a pluralityof cylinders, and machine power is controlled by a power regulating unitwith a connected pressure reservoir, the power regulating unit comprisesa pressure-controller check valve for each of the cylinders, the checkvalves being controlled in synchronism with a regulator valve by the aidof pump valves.
 6. Thermal machine of claim 1, further comprising atleast one of channels located in the equalisation chambers or holeslocated in the piston rods for pressure equilisation.
 7. Thermal machineof claim 1, further comprising a seal between the cylinder and acrankcase of the thermal machine, the seal is an accordion-type spiralhaving a first half made of dextrose and a second half made ofsinistrorse.